ce336 Lab 7 Report

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California State University, Long Beach *

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480

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Mechanical Engineering

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Dec 6, 2023

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1 California State University Long Beach Department of CECEM CE 336 Fluid Mechanics Laboratory Operating Characteristics of Pelton Turbine Experiment #7 Instructor: Dr. Loan Miller Group 3 Group Members: Major(s) Andy Nicky Sok Mechanical Engineering Huu Tran Mechanical Engineering Kevin Alvarez Mechanical Engineering Date: November 3rd, 2023 Fall 2023 Table of Contents 1. Purpose of Study…………………………………………………… 3
2 2. Introduction………………………………………………………… 3 3. Theory……………………………………………………………… 4 4. Equipment and Experimental Set-up………………………………. 7 5. Discussion…………………………………………………………. 10 6. Conclusion………………………………………………………… 21 7. References…………………………………………………………. 24 Purpose of Study
3 The aim of this experiment is to assess the performance of a Pelton turbine in order to gain insight into its operational traits. The efficiency and power output of the Pelton turbine will be evaluated under different constant speeds and operating conditions. Introduction The Pelton turbine is an impulse-type water turbine that converts hydraulic energy from flowing fluid into rotor torque by applying a tangential force directly to the rotor's propeller. It primarily involves changes in kinetic energy with minimal changes in pressure energy. To initiate the turbine, close the hydraulic bench flow control and spear valve. Start the pump, fully open the control valve, apply tension to the band brake, and use a tachometer to measure rotor speed. Simultaneously, record spring balance readings, pressure gauge values, and the time it takes to collect 5 liters of water in the hydraulic bench using a stopwatch. Increase band brake tension four more times to collect a total of five sets of data, including rotor speeds, spring balance readings, pressure gauge data, and water collection times. Then, close the spear valve fully and partially reopen it, repeating all steps to gather another five sets of data with the spear valve partially open. Once all data is collected, calculate the overall turbine efficiency and hydraulic power.
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7 Equipment & Experimental Set-up Figure 1: Hydraulic Bench to adjust the flow rate of the system. Figure 2: Pelton Turbine powered by water.
8 Figure 3: Tachometer to measure the RPM of the Pelton Turbine. Figure 4: Spring Balances to apply tension onto the Turbine.
9 Figure 5: Inlet Water Valve. Figure 6: Pressure Gauge of the inlet Water Valve
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10 Discussion
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13 Sample Calculation
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22 Conclusion
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23 The goal of this experiment is to measure a Pelton turbine's efficiency in order to gain an understanding of its working characteristics. It also aims to familiarize the user with the operating conditions and determine how the turbine's power and efficiency will change at different speeds. Questions 1.Why is the turbine's efficiency curve bell shaped? The Pelton turbine's optimal operating point, at which it works with maximum efficiency, is reflected in its efficiency curve, which has a bell-shaped shape. The efficiency of the turbine reduces as you go from this point by either raising or lowering the flow rate. This is caused by mechanical and hydraulic elements, such as the system's losses and the turbine's capacity to efficiently capture the kinetic energy of the water jet. 2.Compared to the fully open spear valve, how the efficiency of the turbine is affected when the spear valve is partially open. The turbine's efficiency decreases when the spear valve is just partially open as opposed to fully open in the Pelton turbine experiment. This is due to the fact that a partially open spear valve might impede water flow, causing an imbalance between the turbine's design parameters and operating conditions. Because of this, the turbine might not be able to fully utilize the kinetic energy that the water jet has to offer, and the system's higher losses also add to the efficiency drop. Discussion 1.Comment on the shape of the graphs.
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24 The graphs depicting torque, brake power, and turbine efficiency in relation to rotational speed (in Hz) for both fully open and partially open conditions in the Pelton turbine experiment have yielded results in line with expectations. In the fully open condition, the brake power curve exhibits a bell-shaped trend with rotational speed, signifying a peak in power output at an optimal speed, as anticipated. This behavior indicates efficient power generation by the turbine within a specific speed range. In contrast, in the partially open condition, the brake power decreases as rotational speed increases, reflecting the influence of the restricted flow rate and non-optimal conditions. The torque graph, on the other hand, follows an expected decreasing trend with increasing speed in both conditions. The turbine efficiency curve displays lower peak efficiency and maintains a lower overall efficiency in the partially open condition, as foreseen due to the reduced flow rate and non-optimal conditions. These results confirm the unique performance characteristics of the Pelton turbine, with brake power exhibiting different trends under fully open and partially open conditions. 2.Compare at what speed maximum torque, maximum power output occurred when the spear valve was completely open, partially open. The maximum torque was at a rotational speed of roughly 2.6 Hz when the spear valve was fully open. The maximum torque had a rotational speed at roughly 3 Hz when the spear valve was partially open. The maximum power output was at a rotational speed of roughly 7.25 Hz when the spear valve was fully open. The maximum output had a rotational speed at roughly 10.33 Hz when the spear valve was partially open. 3.Discuss if the maximum efficiency is at the same speed when the spear valve was completely open and partially closed.
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25 The optimum efficiency while open happens at 10.92 Hz. The maximum efficiency when partially open was recorded at 10.33 Hz. Achieving peak efficiencies at similar rotational speeds both with the fully open and partially open spear valve suggests that the Pelton turbine's design and operating characteristics are well-suited to a specific range of rotational speeds. The consistency in peak efficiencies can be attributed to the turbine's design, which likely performs optimally within this particular speed range, regardless of the spear valve position. 4. Suggest optimum condition for operation of this Pelton turbine. The optimal condition for a rotational rate of roughly 10-11 Hz in this lab likely results from a combination of factors. It may be a design-specific characteristic of the Pelton turbine used in the experiment, where its buckets and nozzles are most efficient at this speed. Moreover, the consistent experimental conditions, including flow rates and head, could align well with this speed. This data-driven choice of 10-11 Hz demonstrates that the Pelton turbine achieves peak efficiencies at this particular rotational speed, making it the ideal operating point for this specific setup. References
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26 Sultana, R. (2017). Lab # 7: Operating Characteristics of a Pelton Turbine. In CE 336 Fluid Mechanics Lab Manual (pp. 60–66). essay, CSULB Fluid Mechanics Lab Coordinator. Armfield, 2012, “Operating Characteristics of a Pelton Turbine”, Instruction Manual. Munson, B. R., T. H. Okiishi, W. W. Huebsch, A. P. Rothmayer, 2012, “Fundamentals of Fluid Mechanics”, 7th edition, John Wiley, Chapter 8. CE 336 Fluid Mechanics Student Manual, 1993, CSULB.
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